This invention relates to porous, hollow vessels and to methods of manufacturing them. More particularly, this invention relates to an open pore tube made of bonded, resin coated filler particles, which serves as a support tube for cellulose acetate or other types of reverse osmosis membranes.
The major advantage of reverse osmosis as a saline or contaminated water purification process is the low-energy requirements as compared to other processes. The function of a cell for the reverse osmosis process is to bring a saline or contaminated water solution at high pressure into contact with a supported semipermeable membrane.
There are several metals and metal combinations which can be used for the tubular-type membrane support and pressure containing components in a reverse osmosis system. These supports include clad carbon steels with alloys of copper and nickel or stainless steels as the cladding material. These supports easily conform to the pressure requirements of such a system but the initial material cost is very expensive. Such tubular supports must be drilled with holes to permit the pure water to be removed from a saturable medium such as a fabric that is would around the membrane, forming a sump between the support and the membrane. This also adds to fabrication costs.
Porous fiberglass components have been used in reverse osmosis pilot plant operations successfully. Such components while strong and resistant to corrosion are, however, relatively expensive and require elaborate production equipment.
Vondracek in U.S. Pat. No. 3,598,241, taught the use of bonded, resin coated filler particles as a porous, tubular-type membrane support module. The phenolic support modules of that invention, however, have a tendency to occasionally develop stress cracks during curing, and generally require a metal tube surrounding the sand casting as an additional support during operation.
These stress and support problems were solved by Kolek, in U.S. Pat. No. 3,796,314, where an organo silane was used in the resin composition to provide improved tensile and compressive strength properties. Kolek's epoxy compositions, containing silanes and solvents, provided castings having dry compressive strengths and between about 2,400 psi. to 3,460 psi.; vs. about 1,200 psi. to 1,400 psi. dry compressive strengths, and 400 psi. to 800 psi. wet burst strengths for module castings containing the phenolic compositions without salines taught by Vondracek. The Kolek resin formulation did not, however, have a very long shelf life. In addition, the use of solvents presented some problems of solvent entrapment, voids and cracks. And so, there is a need for even better formulations which will impart higher dry compressive and wet burst strengths to reverse osmosis membrane support module castings.